Systems using magnetic-field coupling or electric-field coupling have hitherto been proposed as systems that wirelessly transmit power to portable electronic devices. In the magnetic-field coupling systems, power is transmitted from a primary coil in a power transmitting apparatus to a secondary coil in a power receiving apparatus using the magnetic field. In the electric-field coupling systems, upon proximity (placement) of the power receiving apparatus to (in) the power transmitting apparatus, an electrode in the power transmitting apparatus comes close to an electrode in the power receiving apparatus with a gap interposed therebetween, strong electric field is generated between the two electrodes, and power is transmitted using the electric-field coupling between the electrodes.
In both the magnetic-field coupling and the electric-field coupling, one-to-one relationship is generally established between the power transmitting apparatus and the power receiving apparatus. In order to simultaneously transmit the power to multiple power receiving apparatuses, for example, in the case of the magnetic-field coupling, it is necessary to increase the size of the primary coil in the power transmitting apparatus so that the secondary coils in the multiple power receiving apparatuses are magnetically coupled to the primary coil in the power transmitting apparatus. For electric-field coupling, it is necessary to increase the size of the electrode in the power transmitting apparatus so that the electrodes in the multiple power receiving apparatuses are electrically coupled to the electrode in the power transmitting apparatus.
Patent Document 1 discloses a system concerning a power receiving apparatus to which power is transmitted from a power transmitting apparatus and which is capable of transmitting power to another apparatus. The power receiving apparatus receives alternating-current voltage from the power transmitting apparatus, converts the alternating-current voltage into direct-current voltage to charge a secondary cell with the power, and converts the direct-current voltage into the alternating-current voltage again to transmit the power to another apparatus. Accordingly, it is possible to transmit the power from the one power transmitting apparatus to the two power receiving apparatuses.
Patent Document 1: U.S. Patent Application Publication No. 2013/0026981.
However, for the power receiving apparatus described in Patent Document 1, it is necessary to convert the alternating-current voltage that is received into the direct-current voltage and convert the direct-current voltage into the alternating-current voltage again, there are problems in that loss occurs in the conversion and power transmission efficiency is reduced.